1. Field of the Invention
The present invention relates to a method of determining oxygen precipitation behavior in a silicon monocrystal, to a method of determining a process for producing silicon monocrystalline wafers, and to a recording medium on which is recorded a program for determining oxygen precipitation behavior in a silicon monocrystal.
2. Description of the Related Art
In general, silicon semiconductor wafers for use in fabrication of semiconductor devices such as ICs and LSIs are produced from a silicon monocrystal grown in accordance with a Czochralski method (CZ method). Since a silicon monocrystal contains supersaturated interstitial oxygen, the silicon wafers produced from the monocrystal also contain supersaturated interstitial oxygen. Therefore, if such a silicon wafer undergoes heat treatment in a process of fabricating ICs or the like, interstitial oxygen precipitates in the form of silicon oxides, so that a large number of fine defects are generated inside the wafer.
When such fine defects stemming from oxide precipitates are present within an internal region (bulk region) of a wafer, they desirably act as getter sites that capture heavy metal impurities and the like through so-called intrinsic gettering (IG). By contrast, when such fine defects are present within a semiconductor-device fabrication region in the vicinity of the surface of the wafer, the fine defects hinder operation of semiconductor devices, with the result that the characteristics of the devices degrade, and the production yield is affected directly and adversely.
The above-described problem occurs regardless of whether semiconductor devices are fabricated on a mirror-polished wafer or an epitaxial wafer that is produced through deposition of monocrystalline silicon on a mirror-polished wafer.
Therefore, when semiconductor devices are fabricated on silicon wafers produced in accordance with the CZ method, determining oxygen precipitation behavior within a silicon monocrystal as well as a process for producing silicon monocrystalline wafers in accordance with the determined oxygen precipitation behavior are considerably important for obtaining, at a desired yield, semiconductor devices having desired characteristics.
Thus, the intrinsic gettering (IG) capability of a silicon wafer must be known. In order to express such IG capability, there have been used an amount of precipitated oxygen, which is a decrease in the concentration of interstitial oxygen occurring due to precipitation during a heat treatment process, or a density of bulk defect formed during the heat treatment process. The amount of precipitated oxygen and the bulk defect density are known to strongly depend on concentration of interstitial oxygen within a silicon wafer (initial oxygen concentration within a silicon monocrystal produced in accordance with the CZ method) and conditions of heat treatment that the silicon wafer has undergone (including all thermal histories of silicon, such as a thermal history during growth of the silicon monocrystal in accordance with the CZ method and that of heat treatment that the silicon wafer has undergone in a device-fabricating process).
Accordingly, a proper initial value of oxygen concentration of silicon wafers to be used and conditions of heat treatment for the wafers must be actually investigated in order to ensure that the wafers will have a desired gettering capability during or after a specific device-fabricating process and will have a proper amount of precipitated oxygen and a bulk defect density to thereby increase device yield. Conventionally, a proper initial value of oxygen concentration of silicon wafers and conditions of heat treatment for the wafers have been determined as follows: A large number of wafers having different initial oxygen concentrations and condition of heat treatment performed are prepared and subjected to a heat treatment actually performed in a device-fabricating process to be used or to a heat treatment that simulates the actual heat treatment, under various heat treatment conditions. Subsequently, the amount of precipitated oxygen and the bulk defect density of the wafers are measured in order to determine a proper initial value of oxygen concentration of silicon and heat treatment conditions. The conditions of production of a silicon monocrystal according to the CZ method and the conditions of heat treatment for silicon wafers are determined in order to achieve the determined initial oxygen concentration and the determined heat treatment conditions.
However, when such a conventional method is employed, there must be prepared a large number of wafers having different initial oxygen concentrations and thermal histories, and heat treatment must be performed for a prolonged period of time. Further, since heat treatment conditions vary depending on the type and maker of semiconductor devices to be fabricated, the amount of precipitated oxygen and bulk defect density of wafers must be examined through actual heat treatment whenever the type or maker of semiconductor devices changes. Therefore, considerable time and money are needed in order to determine an initial oxygen concentration and heat treatment conditions for obtaining a proper amount of precipitated oxygen and bulk defect density.
In addition, since an initial oxygen concentration and heat treatment conditions have been determined on the spur of the moment and empirically, accuracy of determination has been insufficient, so that in many cases wafers subjected to an actual production process do not have desired characteristics, due to various factors (e.g., difference in crystal production apparatus and heat treatment apparatus). Therefore, in some cases, it has been difficult to reliably obtain a desired initial oxygen concentration and heat treatment conditions.